The present invention relates to the extrusion of elongated tubular elements, and more particularly to the manufacture of an elongated tubular element for use as a barrel in a writing instrument.
In the production of hollow elongated implements it is well known to extrude a stream of molten thermoplastic material to form the hollow profile. Extrusion processes of this type have been employed using a number of well known materials and have been successful in producing a variety of items, including the barrels for writing instruments.
It is also well known to co-extrude a plurality of layers of material to form such an item, when differing layers are required for the inner and outer surface of the item being produced.
In the manufacture of writing instrument barrels, various configurations of the external barrel surface are employed, generally in an attempt to provide a gripping surface which is more positive, and has a better "feel" to the user. Often these surfaces are formed on a cross-section which is rectilinear, such as that of a triangle, rectangle, hexagon, etc. It is also desirable, in many instances, to provide a material having a softer feel to the user as an external surface of the writing instrument barrel.
There has, therefore, been a need developed to provide a simple operation, or manufacturing process, which would produce a hollow elongated implement such as a writing instrument barrel, having a substantially rectilinear cross-section of a chosen shape by employing a plurality of materials in the process.
It is an object of the present invention to provide a process for the manufacture of a hollow elongated implement which is economical and simple to perform, and which produces a tubular element having a non-circular cross-section of substantially rectilinear form.
Another object of the invention is to provide a co-extrusion process wherein a first material is extruded to produce an elongated element circular in cross-section, and wherein the resultant product contains a plurality of distinct walls that are formed in the tubular element by the extrusion of a second material onto the first material, in accordance with the number of distinct walls required.